Foreign materials may be generated due to several reasons in a manufacturing process of a transparent substrate having a thin thickness, a packaging process, a pattern forming process using the transparent substrate, and the like. In the case in which the foreign materials generated in these process environments are attached onto an upper surface of the substrate, they hinder fine patterns for pixels from being formed on the upper surface in the subsequent process to allow circuit patterns for forming the pixels not to be formed at corresponding positions, thereby causing defective pixels and decreasing a process yield. Therefore, a process of inspecting the foreign materials on the upper surface of the substrate should be performed during or after the manufacturing process.
A lower surface of the substrate contacts a transporting means in order to transport the substrate in a manufacturing process of a flat panel display (FPD) and a semiconductor. Therefore, much more foreign materials may be attached onto the lower surface of the substrate than onto the upper surface of the substrate. Since fine materials having sizes smaller than those of pixels among the foreign materials on the lower surface of the substrate do not have an influence on characteristics of the pixels, the fine foreign materials on the lower surface of the substrate are permitted. Therefore, only the foreign materials on the upper surface of the substrate have been strictly inspected in the manufacturing process of the transparent substrate and the manufacturing process of the FPD and the semiconductor using the transparent substrate.
In the manufacturing process of the FPD and the semiconductor, in order to inspect the foreign materials, a vision inspection method using an image obtained by irradiating light and imaging reflected light by a camera among non-contact inspection methods that do not damage the surface of the substrate has been mainly used. In the case of using the transparent substrate, the light arrives at the lower surface of the transparent substrate, such that reflected light on the foreign materials on the lower surface is also transferred. Therefore, the foreign materials on the lower surface are imaged, thereby making it possible to make an excessive badness decision and have an influence on a manufacturing yield. Therefore, a method of inspecting only the foreign material on the upper surface without being affected by the foreign materials on the lower surface has been required.
A schematic view of an apparatus 10 of detecting a foreign material according to the related art is shown in FIG. 1. Existing methods of detecting a foreign material T1 on an upper surface of a transparent substrate 14 will be described with reference to FIG. 1. There is a method of obliquely irradiating light L having a width enough to be irradiated to both of upper and lower surfaces of the transparent substrate to allow reflected light R to be imaged on foreign materials T1 and T2 on the upper and lower surfaces of the transparent substrate 14, setting a focus of a single imaging device for detection on the upper surface of the transparent substrate 14 and allowing a depth of an imaging lens to be smaller than a thickness of the transparent substrate to allow the foreign material T1 on the upper surface to be clearly viewed and allow the foreign material T2 on the lower surface to be obscurely viewed, thereby separating the foreign material T2 on the lower surface using a contrast difference between the foreign material T1 on the upper surface and the foreign material T2 on the lower surface. Since a contrast difference enough to distinguish an image of the foreign material T1 on the upper surface and an image of the foreign material T2 on the lower surface from each other should be present in order to apply this method, an imaging magnification should be raised or a thickness of the transparent substrate 14 should be thick. In the case of using a high imaging magnification, an inspection visual field is decreased, such that an inspection time becomes excessively long. In addition, in the case of inspecting a thin substrate, a contrast difference is not present, such that it may not be used.
A schematic view of an apparatus 20 of detecting a foreign material according to another exemplary embodiment of the related art is shown in FIG. 2. As shown, the apparatus 20 of detecting a foreign material uses a method of irradiating inclined light L, particularly, a light source having a very narrow width to make light irradiating positions on upper and lower surfaces of a transparent substrate 24 different from each other and then disposing visual fields of a camera 21 for imaging the upper surface and a camera 22 for imaging the lower surface at different positions to distinguish a foreign material T1 on the upper surface and a foreign material T2 on the lower surface from each other. In the case of this method, since the visual fields of the respective cameras 21 and 22 are different from each other, cameras having a lower magnification may be used, such that an inspection time may be decreased. However, also in this method, in the case of a thin substrate, since a distance between light irradiating positions becomes narrow, in the case in which the substrate vertically vibrates by a mechanism for transporting the transparent substrate 24, or the like, the light irradiating positions are horizontally changed, such that an image of the foreign material T2 on the lower surface is captured by the camera 21 for imaging the upper surface. Therefore, this method may also not be applied.
Therefore, a method of removing or significantly decreasing reflected light on the foreign material on the lower surface by allowing inspection light not to arrive at the lower surface has also been used. Japanese Patent Laid-Open Publication No. 1993-196579 has disclosed an apparatus of inspecting a foreign material on a glass substrate used in a manufacturing process of a liquid crystal panel, and more particularly, an apparatus of inspecting only a foreign material on a surface using light having a wavelength at which it is not transmitted through the glass substrate or light having a wavelength at which it has a low transmittance. This technology has an advantage that only the foreign material on the surface of the glass substrate is detected, but has a disadvantage that an expensive laser generating apparatus such as an Excimer laser, a CO2 laser, or the like, is required.